A Universal High-Sensitivity Area-Variation Capacitive Displacement Transducer (CDT) Based on Fringe Effect

Abstract

Capacitive displacement transducers (CDTs) have been widely used in many physical sensors, attributing to high-resolution, simple electricity and easy manufacturing process. Gap-variation CDTs generally have higher displacement resolution due to small electrode gaps but suffer from the pull-in effect, the nonlinear effect and squeeze-film damping; whereas area-variation CDTs have intrinsically good linearity and much smaller slide-film damping. However, the parallel-plate-based area-variation CDTs have the electrode width much larger than the electrode gap with negligible fringe effect; therefore, the sensitivity is limited by periodic electrode numbers. In this paper, we introduce a novel fringe-effect dominated areavariation CDT with a much higher sensitivity within a certain electrode-deployable area. Both theoretical and numerical analysis are applied to investigate the working principle of the CDT design. The proposed fringeeffect-based CDT benefits from a much larger capacitance-to-displacement sensitivity than the traditional periodic array parallel-plate-based CDT, due to the more displacement-sensitive fringe field and more deployable electrode periods. A set of experiments are designed, and the proposed area-variation CDTs are evaluated. Experimental results suggested that the proposed CDT design, which had equal electrode width, separation and gap, could universally be applied to sensors with different featured dimensions either in macroscale or microscale. Angular misalignments with both out-of-plane tilts and in-plane rotations, which affect the output offset and sensitivity, should be minimized or alleviated. The proposed fringe-effect-based CDT are successfully applied to a single-axis in-plane sensing micro-electromechanical systems (MEMS) accelerometer, showing a noise floor as low as 0.25 ng/Hz 1/2 @1 Hz. The corresponding displacement noise of the proposed CDT is 0.1 pm/Hz 1/2 .

An Integrated Gold-Film Temperature Sensor for In Situ Temperature Measurement of a High-Precision MEMS Accelerometer

“…The proposed gold-film temperature sensor was integrated on a MEMS high-precision accelerometer for in situ temperature measurement of the acceleration sensing element, as shown in Figure 11 . The reported MEMS high-precision accelerometer [ 18 ] consists of a silicon-based spring-mass system fabricated by through-wafer etching process [ 19 ] and matching electrodes on both the mass surface and the upper glass layer for area-change capacitive displacement transduction. The gold-film temperature sensor was fabricated on the accelerometer frame simultaneously with the capacitive electrodes.…”

MEMS Microgravity Measurement Module with Nano-g/Hz Noise Floor for Spaceborne Higher-Level Microgravity Scientific Experiment Applications

“…In the MEMS acceleration sensor design, a high-sensitivity area-variation capacitive displacement transducer (CDT) in the previous work has been used. 25 Figure 3 shows the proposed periodic array area-variation CDT. The lower electrodes refer to the positive and negative drive terminals and the upper electrodes represent the pickup terminals.…”

“…In the MEMS acceleration sensor design, a high-sensitivity area-variation capacitive displacement transducer (CDT) in the previous work has been used Figure shows the proposed periodic array area-variation CDT.…”

Design and performance analysis of a MEMS Based Area-Variation Capacitive Accelerometer with Readout Circuit

“…In order to maximize the number of electrodes, the electrodes may be fabricated over the whole surface area of the proof mass. As the spacing between parallel plates capacitors are very small, significant parasitic capacitance occurs between the parallel plate configurations [20]. The mathematical formula to calculate the parasitic plate capacitance is as available in literature [20] as given in equation (7).…”

“…The major benefits of these type accelerometers are strong linearity in displacement variation with capacitance and a wide range of displacement for its operation in an open-loop arrangement, although their manufacturing is a bit complicated. Numerous area change based capacitive accelerometers have recently been produced and described in the literatures [20][21]. By employing a CMOS MEMSbased approach, the microstructure and necessary electronics circuits may be simply constructed on a single wafer.…”